Objective: Interleukin 6 (IL6) has the ability to influence each level of the hypothalamo-pituitary-adrenocortical (HPA) axis. The aim of the study was to test whether IL6 concentration correlates with the adrenal cortex response to ACTH in healthy humans. We postulated that higher basal IL6 concentration would be associated with the higher cortisol response to the stimulation.
Design and methods: Basal IL6 concentration was measured and a low dose (1 microg) ACTH test was performed to assess cortisol response. Twenty-seven apparently healthy subjects (11 male, 16 female, mean age 31.1 years, age range 22-47 years) were included in the study.
Results: Data are presented as mean+/-S.E.M. Basal IL6 level was 0.84+/-0.10 pg/ml. Basal cortisol was 351.9+/-18.3 nmol/l. Maximal cortisol during synacthen test was 653.0+/-20.6 nmol/l. Maximal cortisol increment was 301.1+/-20.0 nmol/l. IL6 concentration was not correlated with basal or maximal cortisol concentration, but correlated significantly with cortisol increment (r=0.63, 95% confidence interval) 0.42-0.83).
Conclusions: In our study, we found that higher basal IL6 concentration is associated with the higher cortisol response to ACTH stimulation. Based on previous research and our data, IL6, even in low concentrations and under physiologic conditions, modulates adrenal cortex responsivity to ACTH. Therefore, it seems that immune modulation of HPA axis is also present under physiologic and not only pathologic conditions.